1. Field of the Invention
This invention relates generally to cooling systems used to cool water in the nuclear reactor of nuclear power generating facilities and, more particularly, to temporary cooling systems which supplement existing cooling systems in such facilities.
2. Prior Art
In nuclear power generating facilities, nuclear fuel and water are contained in a reactor vessel positioned in what is commonly called a refueling cavity or a reactor cavity. During power generation, a primary fluid, normally water, is heated by the nuclear fuel, providing steam for electric power generation. During shutdowns for refueling and other periods when the reactor is not operating, decay heat from the fuel continues to heat the water in the reactor vessel. The water must be cooled to a desired level before fuel may be removed from the vessel and transferred to the spent fuel pool (SFP) of the facility via the reactor cavity. The reactor core is cooled of residual decay heat during shutdown by a permanently installed residual heat removal (RHR) system. It provides heat exchange cooling for decay heat coming from the fuel in the reactor core during shutdown. The heat removal capacity of this system is necessarily large. During normal shutdown, the RHR system is operated for a number of days in order to remove decay heat from the fuel to a point where it may be removed from the core. This is due to the fact that the SFP, the eventual storage place for the fuel, has a permanently installed cooling system, the SFP Cooling System, which does not have sufficient cooling capacity to remove the high level of residual heat immediately following plant shutdown.
Thus, in situations requiring removal of the fuel from the reactor core, the permanent cooling system configuration in present-day nuclear plants requires that the RHR system be operated for a period of days in order to cool the fuel such that it may then be removed to the SFP, then allowing reactor servicing, such as fuel replacement or the decontamination of components such as the reactor recirc system (RRS). The current practice prior to the instant invention was simply to wait until cooling by the RHR system was complete and then proceed to remove the fuel. This increased the facility shutdown period by the number of days required for such cooling, thus increasing the cost of the shutdown operation, lost revenues, as well as the cost of replacement power purchased during the shutdown. The cost of replacement power alone is currently measured in hundreds of thousands of dollars per day. However, permanently increasing the capacity of the SFP cooling system is inordinately expensive and impractical. It is therefore the accepted practice to continue with lengthy prior art cooling methods using the existing systems.